1. Field of the Invention
This invention relates to air seals and more particularly to an air seal between an equipment rack containing air ducts and a removable module or printed wiring assembly having an air passageway.
2. Description of the Prior Art
In the prior art electronic modules such as printed circuit boards have been cooled by forced air. Normally the rack holding the electronic modules also is utilized to contain ducts for carrying air which may be directed through orifices towards the electronic modules and actually through the modules to the other side of the rack for a return air path to an exhaust fan. A very early patent dealing with cross-ventilation is U.S. Pat. No. 2,843,806 which issued on July 15, 1958 to R. J. O'Neill entitled "CROSS-COOLED CABINET FOR ELECTRICAL EQUIPMENT". U.S. Pat. No. 2,843,806 described a cabinet containing air ducts for circulating fresh air along isolated channels to provide a closed cooling system.
An electronic module may, for example, consist of a pair of printed circuit boards which may be riveted or more likely bonded together by means of a frame positioned between the two boards. The frame may enclose the air space between the two printed circuit boards. Holes or ducts in the board frame may permit the passage of cooling air from a supporting rack. One such example is shown in U.S. Pat. No. 3,956,673 which issued on May 11, 1976 to Gordon Seid entitled "PRINTED CIRCUIT MODULES COOLED BY RACK WITH FORCED AIR". In U.S. Pat. No. 3,956,673 a board pair having an enclosed interior air space has air inlet and outlet tubes or hollow pins which extend into openings in the duct carrying air. A grommet is shown for providing a seal between the hollow pin and the duct which may be of rubber or elastomeric material. A small plate is also provided for covering the orifice or grommet when the hollow pin is removed such as when the electronic module is removed.
In U.S. Pat. No. 4,006,388 which issued on Feb. 1, 1977 to W. E. Bartholomew entitled "THERMALLY CONTROLLED ELECTRONIC SYSTEM PACKAGE", a rack is shown for holding electronic modules which has printed circuit boards with air ducts on either side of the electronic modules with openings or orifices in the duct aligned with openings in the electronic module to provide cooling air to the electronic module. The size of the openings in the duct is shown to control the rate of flow of fluid to the electronic module.
In a manufacturing plant at Westinghouse Electric Corporation it has been known to provide a lip seal between a pair of printed circuit boards and a rack containing elongated orifices or openings for providing cooling air to the interior cavity of the pair of printed circuit boards or electronic module. The lip seal was made of rubber and was flexible and extended from the rack conterminous with the elongated orifice which generally extended lengthwise having a uniform width. When the electronic module or printed circuit board was inserted into the rack, the space between the two printed circuit boards was directed or slid along the lip seal such that the lip seal was contiguous with the interior side of both printed circuit boards. For example, a printed circuit board pair would have a connector for making electrical connections on one edge with the two adjacent edges open for the passage of air across the interior space between the boards. The printed circuit board pair would be inserted transverse to the elongated openings or orifices towards the electrical mating connector held in the rack. The lip or flange seals around the orifices of the rack would flex inwardly with each side of the lip seal in contact with the corresponding interior side or surface of the printed circuit board inside the edge as it is being inserted. Normally the printed circuit board pair would be directed along a slot or groove in the rack. The lip seal performed well along the lengthwise direction of the elongated opening or orifice, however, at the ends of the orifice crinkling and buckling of the lip seal was observed providing an inefficient seal from air leaks at the ends. Sometimes the ends were modified by putting in an end stop which would seat against the frame holding the two printed circuit boards together to improve the efficiency of the seal by reducing the air leaks. The crinkling and buckling stems from the aspect ratio of the opening which is large for rectangular slots hence making the end crinkling more secure than in circular type openings.
It is therefore desirable to provide a seal between a removable printed circuit board pair and a rack which is leaktight and leakproof, especially at the ends.
It is further desirable to provide a compression seal which is leaktight and leakproof between a removable electronic module and an equipment rack containing air ducts.
It is further desirable to provide a compression seal which overcomes the problems of crinkling and buckling at the ends of an elongated orifice or slot opening.